Solar project logistics: Calculating the value of an efficient supply chain

solar inverter supply chain

What is a supply chain? It is the flow of all components that go into a given product, and then the flow of that product from its manufacturing origin to its end destination. In a global economy (yes, there still is one, despite Trump’s best efforts) the path from cradle to application can get wildly complex. Inverters are a great example. Modern inverters have thousands of components, integrated into sub-assemblies and then into the inverter product. Sometimes this is happening countries and oceans away from the final point of installation.

As inverters become more homogenous in their basic functions and reliability, finer elements of performance will define the strengths and weaknesses of inverter suppliers. Each supplier’s own ‘supply chain’ is one of those competitive performance variables that buyers and system designers need to consider.

RELATED: How to maximize large-scale PV site value with string design

Why?

An optimized supply chain is valuable to project owners for all of the inherent benefits of efficiency:

  • Costs will likely be lower
  • Lead times will likely be shorter
  • Fewer steps from A to Z means less risk of errors occurring
  • Adjustments will be easier to make on the fly

As it relates to inverter suppliers specifically, developers and EPCs should consider the following.

1. Follow the path of the inverter in reverse, from PV application location, upstream to the site of manufacture.

Does the path make sense? Consider how many stops and warehouses are involved because every stop and transition slathers on another layer of risk and cost.

Beyond the physical transition from place to place, how many changes of ownership are involved in the movement of goods? Is a third-party warehouse used, or a third-party distributor required? Every hand-off means transition of ownership (title and/or process) and usually means added cost and markup by each party. The end owner of the inverter pays for all this, so make sure whether or not you are paying for added risk or added value.

inverter-buyers-guide-300-250

2. Product line strategy – the higher quality inverter could come at a better price point depending on the product line and the supply chain.

How many options, variables and models are you dealing with? Sometimes too many variables means an increased risk of management mistakes and costs, as well as more overhead to manage more parts. Contrast that with a line of a few feature-rich, flexible product models that work for a variety of applications. This can be easier to manage and is helpful for designers.

Now, will feature-rich options add to costs? Not necessarily because of the economies of scale gained from producing fewer models. A localized inventory is more feasible with fewer products to focus on, leading to shorter lead times and ready-to-go stock and reduced inventory investment. Applications engineering, service and life-cycle support is also easier to manage with fewer products for both buyer and seller.

3. Get a full picture of all variables.

Weigh the pros and cons of a supplier manufacturer versus a third-party contract manufacturer. Consider the proximity of the fulfillment hub to the user and the carriers used (is it FedEx or some random company?). Just remember that a fulfillment hub or “Made in the USA” sticker doesn’t give the full picture. The global center of power electronic component production is Asia. So an inverter fully pieced together in Asia that ships to a U.S. fulfillment hub may actually be the most efficient supply chain you could find.

We will also dive into this in MUCH greater detail in this upcoming free webinar. Sign up here.

Utility-Scale String Design

Wed, Jun 20, 2018 2:00 PM EDT

When designing a large site one consideration is String or Central. Both have well defined benefits. Historically, the large utility-scale sites have mainly relied upon central inverters. Now a third option, the Virtual Central, is paving the way for string inverters into this space. In this webinar, we will discuss the benefits and disadvantages to both the distributed and centralized string architectures and how the design choice affects installers, developers and site owners. Sign up here.

— Solar Builder magazine

Power factor boost: Make sure to maximize revenue in design, data monitoring

inverer power factor

Remember the Seinfeld episode where the rental car company took Jerry’s reservation, but still didn’t have a car for him“You know how to take the reservation, you just don’t know how to hold the reservation. And that’s really the most important part: the holding. Anybody can just take them.”

That’s a way to think about monitoring performance of a solar site. (Just go with me here) Anyone can just monitor data, but the key is knowing what to do with it – being proactive versus reactive. Here’s two considerations for being proactive involving inverter selection.

Factoring for power factor

Utility-scale sites often come with reactive power requirements, which usually means reducing the real power produced to provide reactive power support. Because of this, be sure to check the power factor or Max AC Output Power of inverters you spec.

“When you reduce active power, you’re not getting paid at what you designed the system for,” says Sarah Ozga, product manager at CPS America. “We want customers to get paid for the nameplate rating of the inverter and not get dinged for reactive power requirements.”

CPS inverters, for example, come with kVA overhead and will supply 100 percent active power while accommodating reactive power requirements. For a 100-kW inverter, this is listed as 100 kW / 111 kVA at PF greater than 0.9 and 125 kW / 132 kVA at PF greater than 0.95 for the 125-kW inverter. Let’s play out some scenarios.

inverter-buyers-guide-300-250

“If we had a 100 kW/111 kVA or our 125 kW/132 kVA rated inverter and the utility company said we need to run at .95 power factor (PF) we could do this without sacrificing real power (kW),” Ozga says. “For example, if we have enough PV power coming in from the array to produce at max capability on the 125kW/132kVA inverter we would be producing 125kW active power and the apparent power would be 132kVA.”

But what if this overhead wasn’t built into the inverters? If the inverter’s apparent power was capped at 125 kVA, at 0.95 power factor (PF), it would be producing 118.75 kW active power. This is about 7 kW less than it could be producing if it had overhead capacity.

“That’s not real significant for a single inverter but these inverters are generally installed in a multi-MW system,” Ozga notes. “So for a 10 MW site that would be 570 kW, which is a significant loss of power.”

Maximize revenue

Over the life of a system, discovering issues early and fixing them quickly can make a huge difference in site performance and, what everyone is here for, revenue. If an inverter goes down or performance is low, make sure the manufacturer is able to remotely troubleshoot, push updates or make setting changes to the inverters without needing to visit the site, like CPS Ameri-ca can within its Flex Gateway. This gets the inverters back up and performing as it should fast-er and cheaper.

“Whether a company is managing its own data or is using a third party monitoring package it is important for the data to be actively monitored,” Ozga says. “That doesn’t mean someone needs to sit in front a computer watching production graphs all day. Set up automated emails/SMS for alarms or warnings for each site that is managed. These warnings could alert you when an inverter is not performing as expected.”

We will also dive into this in MUCH greater detail in this upcoming free webinar. Sign up here.

Utility-Scale String Design

Wed, Jun 20, 2018 2:00 PM EDT

When designing a large site one consideration is String or Central. Both have well defined benefits. Historically, the large utility-scale sites have mainly relied upon central inverters. Now a third option, the Virtual Central, is paving the way for string inverters into this space. In this webinar, we will discuss the benefits and disadvantages to both the distributed and centralized string architectures and how the design choice affects installers, developers and site owners. Sign up here.

— Solar Builder magazine

Utility-scale solar string design webinar: Distributed vs. centralized strategies

CPS string inverter design

When designing a large site one consideration is string or central inverters? Both have well defined benefits. Historically, the large utility-scale sites have mainly relied upon central inverters. Now a third option, the Virtual Central, is paving the way for string inverters into this space.

Higher powered string inverters, longer strings at 1,500 Vdc and better communication options make these string inverters viable candidates for large projects. In order to know which architecture to choose, first you need to know the benefits and drawbacks of distributed string, virtual central and central systems. One style may not fit all, but the right inverter can fit into multiple architectures.

In this Solar Builder webinar next week, CPS America will discuss the benefits and disadvantages to both the distributed and centralized string architectures and how the design choice affects installers, developers and site owners. Sign up for free here.

— Solar Builder magazine

How to maximize large-scale PV site value with string design

CPS Wirebox Installed before Inverter Body

CPS America inverters come with a separable but integrated wiring box where all of the conductors go in and out.

Service models and technology at the string inverter level is vastly improved from where it was a few years ago. Earlier this week we looked at the value of choosing string inverters over central inverters for projects upward of 20 MW, thanks to 1,500-volt architecture, and then the nuances of approach among virtual centralized string and distributed string.

Choosing string means taking advantage of its positives as much as you can, which means design flexibility and maximizing uptime. If a string inverter or two has to come off line for maintenance, only a fraction of the generation of the system is affected compared to the large chunks connected to a central inverter.

Doubling down on this advantage, for distributed string projects, CPS America inverters come with a separable but integrated wiring box where all of the conductors go in and out. Sold together, every inverter comes with its mated wire box. Four bolts hold the wire box to the inverter body — they slide together with guide pins and one large electrical connector — leaving no wires to play with between the inverter and the wire box.

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“If there is a problem with the inverter, 99 percent of the time, it will be in the inverter not the wiring box,” says Sarah J. Ozga, product manager North America for CPS America. “And what takes so much time when swapping out inverters is disconnecting the wires to remove it. So with the integrated but separable wire box, you never have to touch a wire — just leave the wires and conduits installed in the wire box, disconnect the inverter and slide in the new one in.”

An RMA swap of the inverter body takes only 15 minutes with this approach from CPS. Suddenly, having them dispersed all over the site doesn’t seem as daunting.

There are communication advantages across the market too that improve O&M while simplifying commissioning. Flex Gateway, for example, is a communication card added to just one inverter in the communication daisy-chain of up to 70 inverters. When the inverters are connected to a third-party monitoring system or even simply a router, the CPS Service team can remotely access the inverter for troubleshooting, to change the settings and even update firmware on the connected inverters. This will reduce truck rolls and get systems up and running faster than before.

— Solar Builder magazine

Saving costs with large-scale string inverter design, part 2

CPS string inverter design

During this first week of Attack the Tariff, we are looking at all of the efficiencies to be gained and costs to be saved through large-scale string inverter design. In part 1, we looked at the main economic argument for deploying string inverters in large-scale PV projects. Basically, now that 1,500-volt string inverters in the 100 to 125 kW range are on the market, distributed architecture usually presents a more cost-effective, lower risk large-scale site.

But there are two paths to travel on this road, and which you go down will be site and customer dependent – “virtual central” string and distributed string.

“Virtual central” string design approach is for those looking to keep pieces of what they love about central inverter O&M, but gain the benefits of distributed architecture. You’ll see this with available via Sungrow and CPS America: Instead of every row getting its own inverter, the inverter company partners with a skid integrator to aggregate a group of 20 or more inverters to deploy systems in 2 to 3 MW blocks. This accomplishes several things:

• The obvious O&M benefit of having a ton of inverters centrally located while still reaping the string inverter energy generation benefits and increased uptime.

• A huge reduction in communication wiring costs. This is a big one. The RS485 communication wiring that connects each string inverter could run a tab well north of $10,000. Instead of going row to row with RS485, you’re only going a few feet.

• Installation time is also reduced. “At first that sounds silly, but when you have a 30 MW array out there, that’s a lot of land if you have inverters spread across the whole thing,” Ozga says.

But virtual central string will also need combiner boxes out in the array, which is an added cost that offsets the benefit of the centralization of the skid and affects the O&M picture.

inverter-buyers-guide-300-250

Distributed string is just what you think it is, with string inverters distributed at the end of each array. The differences can often be fractions of percentage points, with the main considerations being: experiences with DC and AC wiring, labor rates, trenching, DC and AC cabling costs, voltage drop calculations, data monitoring costs, etc.

While communications wiring is reduced in virtual central systems, CPS has designed the distributed string inverters to drastically reduce this cost as well. Both the 100- and 125-kW 1500-volt distributed string versions include power line communication (PLC) as one communication method. This feature eliminates the cost for wiring RS485 throughout the array.

Choosing among distributed string or centralized string options will be site and customer specific. CPS America provides both options, and Ozga says some customers see the wiring costs are greater in distributed while others see them higher in an aggregated virtual central system. It is worth the exercise to calculate both scenarios in full to see how they pencil out for every project.

“We’ve decided to offer both for any customers that feel they are not seeing the savings and want to stay distributed, but I think it is a decision that comes down to system size,” says Sarah J. Ozga, product manager North America for CPS America.

There is even more with the O&M equation for true distributed string architecture, which we’ll look at in part 3 on Friday.

We will also dive into this in MUCH greater detail in this upcoming free webinar. Sign up here.

Utility-Scale String Design

Wed, Jun 20, 2018 2:00 PM EDT

When designing a large site one consideration is String or Central. Both have well defined benefits. Historically, the large utility-scale sites have mainly relied upon central inverters. Now a third option, the Virtual Central, is paving the way for string inverters into this space. In this webinar, we will discuss the benefits and disadvantages to both the distributed and centralized string architectures and how the design choice affects installers, developers and site owners. Sign up here.

— Solar Builder magazine